This invention relates to a turbo-machine control system and more precisely to a digital electronic back-up control system.
Modern aircraft engines are driven by an electronic engine control system, which controls the thrust and the torque delivered by the engine. Usually such systems are designed using a microprocessor, allowing the control algorithms to be implemented by software.
The electronic engine control system must at least detect an overspeed of the turbo-machinery that could be fatal for it. In such a case, it is important to cut off the fuel flow.
These control algorithms control the spool speed of the turbo-machinery by scheduling the burn fuel flow through a hydromechanical fuel metering unit. Sensors on the turbo-machine supply information on what is needed to drive the turbo-machine. The control algorithms which are running on the microprocessor provide the proper burn fuel flow using all the inputs.
In case of emergency, it is important to rely on a back-up system. Such back-up systems will provide the same information to the fuel metering unit. Two different configurations are now available.
In the first configuration available, the back-up system is a hydromechanical back-up system. In this configuration, the back-up system controls the burn fuel flow through a mechanical, hydraulic or pneumatic control system.
In the other configuration available, the back-up system is another electronic engine control system identical to the main electronic control system. Such a parallel system is named a dual channel electronic engine control system. A special algorithm might be used to ensure a proper switch between one channel and the other.
Furthermore, the use of a hydromechanical back-up control increases the weight and the complexity of the control system, thus this is not an advantageous solution for a use in an aircraft.
When a failure of the electronic engine control system is detected, a sudden transition from the electronic engine control system to a back-up engine control system can be harmful to the turbo-machine. In fact, if the fuel flow computed by the electronic engine control system at its failure is far different from the fuel flow computed by the back-up engine control system when it is enabled, great damages can occur due to a the non-continuous supply of fuel.
Therefore there is a need for a reliable back-up control system that will smoothly take control of the turbo-machinery in the event of a failure.
It is an object of the present invention to provide an electronically operated back-up system for a turbo-machine to be use in case of failure of the main electronic engine control system.
It is another object of the present invention to provide an electronically operated back-up system for a turbo-machine that is not a duplication of the main electronic engine control system.
It is an object of the present invention to provide an electronically operated back-up system for a turbo-machine that is able to start the engine.
It is another object of the present invention to provide an electronically operated back-up system for a turbo-machine that is able to guarantee a minimum fuel flow in the engine in order to avoid a flameout.
It is another object of the present invention to provide an electronically operated back-up system for a turbo-machine that is able to avoid power increase or decrease in the engine during the transfer to the back-up control mode.
According to one aspect of the invention, there is provided a back-up system for controlling a turbo-machine via a fuel metering unit when the electronic engine control of the turbo-machine fails, which comprises a back-up burn fuel flow calculator, the back-up fuel flow calculator receiving at least the amount of fuel requested by the operator signal of the turbo-machine and the actual spool speed of the turbo-machine and computing an amount of fuel to provide to said turbo-machine in order to adjust its speed to obtain a spool speed equivalent to the amount of fuel requested by the operator signal, a last burn fuel flow storage, the last burn fuel flow storage storing the last burn fuel flow value provided by the electronic engine control before its failure, a transitional burn fuel flow manager, the transitional burn fuel flow manager receiving the amount of fuel computed by the back-up burn fuel flow calculator and the last burn fuel flow value stored in the storage and providing an amount of fuel to provide to the fuel metering unit.
According to another aspect of the invention, there is provided a method for determining a burn fuel flow value, comprising the steps of receiving a current fuel flow value provided to a fuel metering unit of a turbo-machine from a main burn fuel flow calculator, storing the current fuel flow value in a memory upon detection of a malfunction of the main burn fuel flow calculator, calculating a transitional value using the stored fuel flow value and a back-up burn fuel flow value received from a back-up burn fuel flow calculator and outputting the transitional value to said fuel metering unit.
According to another embodiment of the present invention, there is provided a method for determining a burn fuel flow value for an aircraft turbo-machine in case of a malfunction, the method comprising the steps of receiving a current fuel flow value from a main burn fuel flow calculator, storing the current fuel flow value prior to the malfunction, calculating a back-up burn fuel flow value using sensor readings from the aircraft and initially the stored current fuel flow value, wherein the calculating using an algorithm which is different from an algorithm used for calculating the main burn fuel value, the back-up burn fuel flow value having a smooth transition between the current fuel flow value prior to the malfunction and future burn fuel flow values and outputting the back-up burn fuel flow value to a fuel metering unit.